The Relationship Between RNFL And Tumor Extension, Optic Chiasm Thickness

Background and ObjectiveThe compression of optic chiasm by pituitary adenomas (Pas) can cause the axonal degeneration of optical nerve, resulting in the thickness of retinal nerve fiber layer (RNFL). So RNFL can structurally measure the patients’visual field (VF) loss, progress and prognosis. Also there are several studies having documented that this problem has relationship with the tumor volume and optic chiasm compression. This study armed at the relationship between RNFL and optic chiasm thickness, tumor extension, and further evaluating whether magnetic resonance imaging (MRI) which is used to measure optic chiasm thickness and tumor extension can offer a reliable prediction of RNFL thickness.Patients and methodsFifty-seven patients who were clinically and pathologically diagnosed with Pas in Huashan Hospital, and underwent MRI detecting compressed optic chiasm pre-operation were included from July 2010 to December 2013.We measured the suprasellar height of Pas using sagittal (Hs) and coronal (He) MRI. In addition, the optic chiasm thickness was assessed in coronal MRI. The findings correlated with RNFL were measured using optic coherence tomography (OCT), with the VF defect (VFD) were measured using static visual field perimetry with Humphrey perimeter. Patients were divided into two groups according to the result of Humphrey:patients without VFD and patients with VFD. The latter group was divided into two subgroups: patients with unilateral VFD and patients with bilateral VFD. In patients without VFD, the cited RNFL thickness by OCT was the mean average of both eyes; in patients with unilateral VFD, the cited RNFL thickness by OCT was the mean of sick eye; in patients with bilateral VFD, the cited RNFL thickness by OCT was calculated from the worse eye. T-test was used to compare optic chiasm thickness, Hs, He and RNFL measurements between these groups. Pearson correlation was conducted to evaluate the relationship between tumor extension, optic chiasm thickness and RNFL thickness:1. The relationship between RNFL thickness and Hc/Hs.2. The relationship between RNFL thickness and optic chiasm thickness.ResultsA total of 57 patients (25 female,32 male) were studied. Twenty-one (36.8%) had no VFD, twenty-nine (50.9%) had bilateral VFD, and seven (12.3%) had unilateral VFD.1. Optic chiasm thickness, Hc/Hs, and RNFL thicknessMean optic chiasm thickness was 1.52±0.27mm, mean He was 23.42±5.54mm, mean Hs was 22.07±5.10mm, and mean RNFL thickness was 66.90±10.61μm. In patients without VFD, mean optic chiasm thickness was 1.76±0.18mm, mean He was 20.17±3.32mm, mean Hs was 18.12±3.32mm, and mean RNFL thickness was 72.91±10.80μm; in patients with VFD, mean optic chiasm thickness was 1.37± 0.21mm, mean He was 25.32±5.72mm, mean Hs was 24.37±4.53mm, and mean RNFL thickness was 63.38±8.89μm. Those four indicates in the two groups were significantly different.In patients with bilateral VFD, mean optic chiasm thickness was 1.38±0.22mm, mean He was 25.67±6.23mm, mean Hs was 24.62±4.95mm, and mean RNFL thickness was 62.99±9.18μm; in patients with unilateral VFD, mean optic chiasm thickness was 1.34±0.19mm, mean He was 23.87±2.51mm, mean Hs was 23.33± 1.95mm, and mean RNFL thickness was 65.03±8.01μm. There was no significant difference being found between the two groups above.Compare with the bilateral VFD group, the patients without VFD had a strong difference in those four aspects. Also between the unilateral VFD group and the without VFD group, they were statistically different in Hs, Hc, optic chiasm thickness and RNFL, but in RNFL the difference was not significant.2. The relationship between RNFL thickness and Hc/Hs, optical chiasm thicknessUnder the linear correlation analyses (Pearson’s coefficient), between RNFL thickness and Hc/Hs, there was a strong statistically negative correlation in patients with bilateral VFD (Hc:r=-0.714, p= 0.000; Hs:r=-0.659, p= 0.000), while there was no significant correlation being found in patients with unilateral VFD (Hc:r=-0.291, p= 0.527; Hs:r=-0.800, p= 0.865), neither in patients without VFD (Hc:r= 0.450, p= 0.141; Hs:r= 0.074, p= 0.749).Between RNFL thickness and optic chiasm thickness, it documented a positive correlation in the bilateral VFD (r=0.796, p=0.000), but non-correlation in the unilateral VFD (r=0.510, p=0.243), and in the normal VF (r=0.047, p=0.840).Conclusion1. Optic chiasm thickness, suprasellar height (Hc and Hs) of Pas and RNFL thickness were significantly different between patients with normal VF and with VFD. Patients with VFD, no matter bilateral VFD or unilateral VFD, were higher in tumor extension, thinner in optic chiasm and in RNFL.2. Between patients with bilateral VFD and unilateral VFD, there was no significant difference in optic chiasm thickness, Hc/Hs and RNFL thickness.3. Only in the bilateral VFD patients, RNFL had a positive correlation with optic chiasm, and a negative correlation with He and Hs. In the normal VF or unilateral VFD patients, there was no correlation between RNFL thickness and optic chiasm, Hc/Hs.